Refresh Python lesson 0 installation guide

[MatthewRayUK]

• Removed two links to diveintopython3.problemsolving.io - the domain has lapsed and now redirects visitors elsewhere. Replaced with the official Python docs under Further reading
• Windows steps now use the Python install manager, which python.org recommends (the Python docs mark the old installer as deprecated)
• Removed outdated Python 2 references on Mac, and updated the installer file name
• Added a Chromebook section on turning on Linux, plus troubleshooting for work and school Chromebooks
• Removed the CentOS section (end of life in 2024), added Fedora, and added sudo to the Linux commands
• Commands are now python3 on Mac, Chromebook and Linux, and python on Windows
• Added an "If it goes wrong" section covering common install problems
• Added Objectives, Goal, Further reading, a link to lesson 1 and the codebar sign-off, to match the other tutorials
• Made formatting consistent - buttons to click in bold, things to type in code formatting
• Updated the version to 3.14.7

[KimberleyCook]

Aweeeeesome 🎉